This invention relates to the preparation of polychloro copper phthalocyanine and, particularly, to an improved process for preparing polychloro copper phthalocyanine by the eutectic method.
Polyhalo metal phthalocyanines have been produced by a variety of methods. What appears to be the first attempt to produce halogenated phthalocyanines by halogenation of the synthesized phthalocyanine is described in British Pat. No. 461,268. As halogenating agents therein it is proposed to employ normally liquid halogenating agents, such as sulfuryl chloride, thionyl chloride, bromine, or liquid chlorine. The reaction is normally carried out in a sealed vessel, and at a temperature between 230.degree. and 300.degree. C. Such halogen carriers as aluminum chloride are used in limited quantities, but the bulk of the reaction medium consisted of the liquid halogenating agent. In other words, the halogenating agent is depended upon to supply the liquid medium for the reaction and the process is consequently limited to such halogenating agents as are liquids under the reaction conditions, or to such conditions of operation (e.g., autogenous pressure) as will maintain the halogenating agent in liquid condition. Although the process of British Pat. No. 461,268 produces polyhalo phthalocyanines which were adequate in many respects, the process is not successful in introducing beyond about 12.3 atoms of halogen per molecule, and that only by starting with a tetrachloro or octachloro phthalocyanine can the halogen content of the phthalocyanine be raised to about 13 or 14 atoms per molecule.
An attempt to correct the deficiencies of British Pat. No. 461,268 is described in U.S. Pat. No. 2,247,752. This patent describes a process for preparing highly halogenated metal phthalocyanines by halogenating the metal phthalocyanine in a reaction medium of molten inorganic halide. This process is commonly referred to in the art as the "eutectic" process for preparing polyhalo metal phthalocyanines. The halogenation is normally accomplished by passing gaseous halogen, particularly chlorine, through the molten inorganic halide. Although the amount of gaseous halogen used in this process is not nearly as excessive as that of the liquid halogenating agent of British Pat. No. 461,168, in practice at least 30% excess must be employed because some gaseous halogen bubbles through the molten reaction medium and does not react. By this process it is possible to produce metal phthalocyanines, particularly copper phthalocyanine, having over 13 atoms of chlorine per molecule up to, in some cases, the theoretical maximum of 16 atoms per molecule. The polychloro copper phthalocyanine so produced exhibits a bright green shade which was previously unavailable in colors of the phthalocyanine series.
Although the polychloro copper phthalocyanine produced according to U.S. Pat. No. 2,247,752 is adequate for many applications, the yield, particularly in the case of highly chlorinated copper phthalocyanines, is undesirably low and the pigmentary properties of the product, particularly strength, are not as high as desirable for high quality pigmentary applications. I have found that the problems associated with this process are due predominantly to the formation of tetrachlorophthalimide, a colorless compound useless as a pigment. Tetrachlorophthalimide, which is formed upon contacting the reaction medium with water, cannot be converted to the polychloro copper phthalocyanine and must be extracted from the polychloro copper phthalocyanine with alkali.
To overcome the disadvantages of the conventional eutectic process, I have developed an improved eutectic process which prevents the formation of tetrachlorophthalimide and thus provides for the preparation of a highly chlorinated copper phthalocyanine without substantial yield loss and contamination.